The present invention is based on a priority application EP 06 291 097.1 which is hereby incorporated by reference.
The present invention relates to a method of providing resource admission control to a packet flow in a communication network, and an access controller to execute said method.
As IP networks are increasingly used to transport real-time, in-elastic traffic with hard QoS (=Quality of Service) guarantees, appropriate traffic management becomes increasingly challenging (IP=Internet Protocol). Proactive traffic management schemes rely on RAC (=Resource Admission Control) for new sessions that have to be set up. The aim of RAC is to determine if the network can carry the new session at the appropriate QoS without impacting the QoS specifications of already ongoing real-time sessions. Especially the latter is of extreme importance in IP networks as in the (pre-dominantly used) diffserv-like model, a new session that is admitted to run at the highest QoS class level while there are not sufficient resources in the network to sustain that session, will not only be adversely affected by that lack of resources, but will also impact the other sessions running at the same QoS class level.
Current envisaged solutions either assume that the network is dimensioned in a way that no problems can arise, or rely on a central resource manager having a (theoretical) model of the available resources in the network, and which is queried for acceptance on each new session set-up, e.g. TISPAN RAC Functions and Architecture (TISPAN=Telecoms & Internet converged Services & Protocols for Advanced Networks).
The assumption of over-dimensioning the network is not realistic for a variety of reasons, such as: with the ever growing amount of traffic, it is not trivial to assure that there will be always enough resources in the network to avoid any congestion problems. Even if the average traffic would be predictable, mass events such as tele-voting will cause peaks of traffic in which problems will occur. For economical reasons, access and aggregation networks are not non-blocking and will cause traffic congestion if no measures are taken.
In the model with a central resource controller, the central entity has to be queried to accept or deny each new session request. This leads to the following drawbacks. Increased complexity and increased latency in session set-up: the signalling flow for setting up the session must be interleaved with the resource queries to the resource controller, adding to the end-to-end set-up delay (Multiple round-trip signalling plane interactions).
Another drawback is that a failure of access to the central resource controller services leads to unavailability of the service. As no resources can be granted, all new sessions will be rejected.
Still another drawback is that the resource controller uses a (pre-configured) model of the network resources upon which it grants or refuses new session requests (resource counting). A change in network topology, maintenance activities, or network link failures require a change to the model, which is not updated in real-time. This makes the network resource controller work with a model that does not fit reality for a certain amount of time.
Another drawback is that RAC-based solutions can lead to underutilization of available network capacity as an application will tend to reserve more resources than effectively needed, as, e.g. with non-CBR traffic based services (CBR=Constant Bit Rate).